Small, touch-enabled, screen devices, such as mobile cellular telephones and personal digital assistants (“PDAs”), are increasing in popularity. A typical small, touch-enabled, screen device is a limited function microcomputer provided with a pressure sensitive liquid crystal diode (LCD) display (a touch pad or a touch screen) for input and output (I/O). Small screen devices are useful for many purposes including voice and wireless Internet communication, scheduling, and note taking. Often the primary input means for these small screen devices is via the pressure sensitive LCD display with a limited-size keypad. As these portable devices become smaller and more specialized, continuous written input has become more difficult and less practical. Pen-based user interfaces are attractive because they are scalable (i.e., only small reductions in size can be made to keyboards before they become awkward to use) and offer the pointing capabilities of a touch-screen or mouse. Furthermore, when compared to voice-based interfaces, pen-based input takes place in private, in silence without disturbing bystanders, and is insensitive to acoustic noise in the environment.
Manual input on small screen devices, such as mobile cellular telephones and personal digital assistants (“PDA”) generally consists of one or more “ink traces” for user input. As is known in the art, an ink point is an element in the stream of data recorded by a real-time digitizer of writing and a trace is a sequence of contiguous ink points. An ink trace is a complete pen-down movement bounded by two pen-up movements or a complete pen-up movement. A sequence of traces accumulates to meaningful units, such as characters and words.
Because of the limited size of the screen relative to the size of the written input, there are inherent complications associated with the physical size of the input area on small screen devices. For small screen sized devices such as of PDAs, input interfaces often referred to as write-anywhere user interfaces allow users to write two or three lines at a time where each line may only contain two or three words. This limited word entry capability limits the realistic volume of writing and prevents continuous uninterrupted longhand entry. Further, these write-anywhere interfaces are problematic because it is difficult to differentiate whether the stylus is acting as a pointer, for clicking on application icons and the like, or an inking instrument for text entry. A common solution involves an un-natural “tap and hold” scheme wherein the pen has to be maintained down without dragging it for a certain amount of time in order to get the stylus to act temporarily as a mouse. This can lead to text input errors and the attendant aggravation and input delays caused by such errors.
In the prior art there exists several options to increase the writing space available: the user can manually scroll the writing area, the application can automatically scroll up the writing area when ink traces are detected at the bottom of the screen, or the application can convert the ink traces into a scaled down representation that clears part of the writing area. Each of the current prior art options has problems associated with them that require interruptions in the writing input. Manually scrolling the input area requires the user to move the cursor away from the input area and to a scroll bar or equivalent movement area to manually scroll the writing area. Automatically scrolling by an application detecting ink traces at the bottom of the screen requires interruptions during the detection and scrolling process. Finally, automatically converting the ink traces into a scaled down representation requires interruptions during the conversion process since a portion of the writing area is cleared.